1. Field of the Invention
The present invention relates to a magnetic tape cartridge in which a single tape reel with magnetic tape wound thereon is rotatably housed within a cartridge case, and more particularly to a magnetic tape cartridge, which has a cartridge case equipped with upper and lower cases of synthetic resin fastened together and a tape leader opening formed in the side walls of the upper and lower cases, and in which a tape leader pin firmly attached to the leading end of the magnetic tape is detachably held in an upright state between the upper and lower case so that it faces the tape leader opening.
2. Description of the Related Art
In magnetic tape cartridges, which are being used as storage media that are employed in external storage units for computers, etc., there is known a type where a single tape reel with magnetic tape wound thereon is rotatably housed within a cartridge case. This magnetic tape is employed to archive data for computers, etc. Since important information has been stored, the magnetic tape cartridge is constructed so that problems, such as tape jamming, etc., do not occur and that the magnetic tape is not pulled out of the cartridge case inadvertently.
The magnetic tape has a tape leader pin firmly attached to the leading end thereof. When this magnetic tape cartridge is loaded into a recording-reproducing unit, a leader-pin catching member on the side of the recording-reproducing unit engages the tape leader pin and pulls out the magnetic tape from the cartridge case. On the other hand, when the magnetic tape cartridge is unloaded from the recording-reproducing unit, the magnetic tape is rewound on the tape reel and the tape leader pin is returned into the cartridge case by the leader-pin catching member. The cartridge case is formed by fasten in upper and lower cases of synthetic resin together with a plurality of small screws, and has a tape leader opening, which is formed in the side walls of the upper and lower cases. The tape leader pin is detachably held at the upper and lower ends thereof by a leader-pin holding spring so that it faces the tape leader opening.
The above-mentioned tape leader pin is illustrated in FIG. 1. This tape leader pin 5 is constructed of a pin main body P of, for example, metal and a tape clamp member 5e of synthetic resin. The pin main body P consists of a tape clamp portion 5a formed between a pair of inner flanges 5b, 5b, small-diameter shaft portions 5c, 5c respectively formed outside the inner flanges 5b, 5b, and outer flanges 5d, 5d respectively formed outside the small-diameter shaft portions 5c, 5c. In addition, the tape clamp portion 5e has a C-shaped cross section and is elastically fitted onto the outer periphery of the tape clamp portion 5a of the pin main body P, whereby the leading end portion of the magnetic tape 6 is clamped between the tape clamp member 5e and the tape clamp portion 5a. 
In the magnetic tape cartridge, on the other hand, the magnetic tape 6 is completely wound on the tape reel during non-use of the cartridge, and the upper and lower flanges 5d, 5d of the tape leader pin 5 are housed in upper and lower leader-pin housing recesses formed near the tape leader opening and are locked and held by the aforementioned leader-pin holding spring that elastically abuts the upper and lower flanges 5d, 5d. In this manner, the tape leader pin 5 is locked and held in an upright state. If the magnetic tape cartridge is loaded into a recording-reproducing unit that uses this magnetic tape cartridge, the upper and lower small-diameter shaft portions 5c, 5c of the tape leader pin 5 are caught by a leader-pin catching member provided in the cartridge drive mechanism of the recording-reproducing unit, and the magnetic tape 6 is introduced into a tape traveling path formed within the recording-reproducing unit.
As stated above, the upper and lower cases constituting the cartridge case of the magnetic tape cartridge are usually fastened together by four small screws. In the case where the upper and lower cases are fastened together by small screws, the shank portion of each small screw requires a thickness of some magnitude or greater to form threads therein. Furthermore, for these small screws, one of the upper and lower cases requires boss portions each having a through bore, while the other requires boss portions each having a threaded bore. Because of this, space for these boss portions has to be assured.
Near the leader-pin holding portion, however, there is no space to provide boss portions which are used for fastening small screws, in order to avoid interference with the leader-pin catching member of the recording-reproducing unit and assure a tape traveling path for magnetic tape. Because of this, and also because of the presence of the tape leader opening, the force fastening the upper and lower cases together is weaker near the leader-pin holding portion than at other parts.
Therefore, when a strong shock is exerted on the cartridge case by its being dropped, etc., or in the case when a force that opens the upper and lower cases is exerted near the tape leader opening, there is a problem that (1) the upper and lower cases in that portion will be moved away from each other, (2) the tape leader pin being held between the upper and lower cases will fall out of the leader-pin holding portion of the cartridge case and will be tilted, and (3) the catching of the tape leader pin by the leader-pin catching member of the drive mechanism of the recording-reproducing unit will become impossible.
To prevent the falling of the tape leader pin due to such a strong shock, the joining surfaces of the upper and lower cases of the cartridge case can be welded over the entire circumference. However, welding the joining surfaces of the upper and lower cases is undesirable with regard to disassembly, because there is a need to disassemble the cartridge case and take out the magnetic tape with important information along with the tape reel and then put them into a new cartridge case, in the event of an unforeseen accident, or after long-term use.
Furthermore, because the force fastening the upper and lower cases is weaker near the leader-pin holding portion than other parts, there is another problem that the tape leader pin being held between the upper and lower cases will fall out of the leader-pin holding portion by the moment of inertia of the tape leader pin, when shock is exerted on the cartridge case by its being dropped, etc.